US 7857875 B2
A method for start-up and shut down of a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst is disclosed. Also disclosed are a computer programmed to start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst or a program storage medium encoded with instruction that, when executed by a computer, start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst.
1. A method for lighting off an oxidizer in a fuel processor, comprising:
purging a reactor of the oxidizer with air at an initial temperature;
generating an ignition heat in at least a portion of the purged oxidizer reactor;
introducing a fuel to the heated region of the oxidizer reactor, the resulting mixture of the fuel and the air remaining below the lower explosive limit of the fuel; and
heating the oxidizer reactor containing the fuel/air mixture to an operating temperature.
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The present invention is a divisional application of U.S. Ser. No. 10/408,001, filed Apr. 4, 2003 now U.S. Pat. No. 7,081,144, the complete disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention is directed to a fuel processor, and, more particularly, to a control system for a fuel processor.
2. Description of the Related Art
Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion for use as fuel for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Thus, many types of fuels can be used, some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a relatively pure hydrogen stream used to fuel the fuel cell.
The invention comprises a method for start-up and shut down of a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst.
In a first aspect, the invention includes a method for starting up an autothermal reformer in a fuel processor, comprising: purging the reactor of the autothermal reformer with a fuel above the upper explosive limit of a process feed stream comprising the fuel at an initial temperature; maintaining a non-pyrophoric shift catalyst of the autothermal reformer at a temperature sufficient to prevent condensation of water therein; heating the purged autothermal reformer reactor to the light off temperature of the non-pyrophoric shift catalyst while continuing to flow the fuel therethrough; introducing air to the heated autothermal reformer reactor to produce an air and fuel mixture exceeding the upper explosive limit of the fuel; and heating the autothermal reformer reactor to an operating temperature.
In a second aspect, the invention includes a method for lighting off an oxidizer in a fuel processor, comprising: purging a reactor of the oxidizer with air at an initial temperature; generating an ignition heat in at least a portion of the purged oxidizer reactor; introducing a fuel to the heated region of the oxidizer reactor, the resulting mixture of the fuel and the air remaining below the lower explosive limit of the fuel; and heating the oxidizer reactor containing the fuel/air mixture to an operating temperature.
In a third aspect, the invention includes a method for shutting down an autothermal reformer employing a non-pyrophoric shift catalyst in a fuel processor, comprising: terminating air flow to the autothermal reformer reactor; terminating water flow to the autothermal reformer reactor after terminating the air flow; purging the autothermal reformer reactor with a fuel; and allowing the autothermal reformer reactor to cool to a shutdown temperature.
In a fourth aspect, the invention includes a method for shutting down an oxidizer for use with an autothermal reformer employing a non-pyrophoric shift catalyst, comprising: terminating the flow of the fuel to a reactor of the oxidizer; purging the oxidizer reactor with air until the temperature within the oxidizer reactor reaches an ambient temperature; and terminating the air flow to the purged oxidizer reactor.
In still other aspects, the invention includes a computer programmed to start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst or a program storage medium encoded with instruction that, when executed by a computer, start-up or shut down a fuel processor including an autothermal reformer employing a non-pyrophoric shift catalyst.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present invention is generally directed to method and apparatus for controlling a “fuel processor,” or “reformer,” i.e., an apparatus for converting hydrocarbon fuel into a hydrogen rich gas. The term “fuel processor” shall be used herein. In the embodiment illustrated herein, the method and apparatus control a compact processor for producing a hydrogen rich gas stream from a hydrocarbon fuel for use in fuel cells. However, other fuel processors may be used in alternative embodiments. Furthermore, other possible uses are contemplated for the apparatus and method described herein, including any use wherein a hydrogen rich stream is desired. The method and apparatus may also be used in embodiments not applicable to the production of gas streams. Accordingly, while the invention is described herein as being used in conjunction with a fuel cell, the scope of the invention is not limited to such use.
As previously mentioned, the fuel in the illustrated embodiment is natural gas, but may be some other type of hydrocarbon. The hydrocarbon fuel may be liquid or gas at ambient conditions as long as it can be vaporized. As used herein the term “hydrocarbon” includes organic compounds having C—H bonds which are capable of producing hydrogen from a partial oxidation or steam reforming reaction. The presence of atoms other than carbon and hydrogen in the molecular structure of the compound is not excluded. Thus, suitable fuels for use in the method and apparatus disclosed herein include, but are not limited to hydrocarbon fuels such as natural gas, methane, ethane, propane, butane, naphtha, gasoline, and diesel fuel, and alcohols such as methanol, ethanol, propanol, and the like.
The operation of the fuel processor 102 and the fuel cell 104 are inter-related in the illustrated embodiment. The fuel processor 102 provides a hydrogen-rich effluent stream, or “reformate,” as indicated by the graphic 108, to the fuel cell 104. The reformate 108, in the illustrated embodiment, includes hydrogen and carbon dioxide and can also include some water, unconverted hydrocarbons, carbon monoxide, impurities (e.g., hydrogen sulfide and ammonia) and inert components (e.g., nitrogen and argon, especially if air was a component of the feed stream). Note, however, that the precise composition of the reformate 108 is implementation specific and not material to the practice of the invention.
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Note that the shift 250 d employs a non-pyrophoric shift catalyst, not shown. Non-pyrophoric shift catalysts are those that typically do not increase in temperature more than 200° C. when exposed to air after initial reduction. Non-pyrophoric shift catalysts may be based on precious metals, e.g., platinum or non-precious metals, e.g., copper. One commercially available non-pyrophoric shift catalyst suitable for use with the present invention is the SELECTRA SHIFT™ available from:
The computing apparatus 300 illustrated in
Thus, at least some aspects of the present invention will typically be implemented as software on an appropriately programmed computing device, e.g., the computing apparatus 300 in
Some portions of the detailed descriptions herein may consequently be presented in terms of a software-implemented process involving symbolic representations of operations on data bits within a memory in a computing system or a computing device. These descriptions and representations are the means used by those in the art to most effectively convey the substance of their work to others skilled in the art. The process and operation require physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical, magnetic, or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantifies. Unless specifically stated or otherwise as may be apparent, throughout the present disclosure, these descriptions refer to the action and processes of an electronic device, that manipulates and transforms data represented as physical (electronic, magnetic, or optical) quantities within some electronic device's storage into other data similarly represented as physical quantities within the storage, or in transmission or display devices. Exemplary of the terms denoting such a description are, without limitation, the terms “processing,” “computing,” “calculating,” “determining,” “displaying,” and the like.
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In the illustrated embodiment, the reactor 224 is purged (at 412) with air 118 supplied from the air subsystem 126 at a rate of 200 L/min for a minimum of 15 minutes, or at least three reactor volumes of air 118. As those in the art having the benefit of this disclosure will appreciate, this rate and duration are a function of the volume of the reactor 224. Accordingly, the rate and duration are implementation specific, and other rates and durations may be applied in alternative embodiments. The content of the reactor 224 at this point is 100% air for the illustrated embodiment. However, this is not necessary to the practice of the invention. The objective is to purge the reactor 224 to just below the lower explosive limit (“LEL”) of the fuel 112 that is to be subsequently introduced. Other air flow rates, durations, and volumes therefore may be used in alternative embodiments.
The oxidizer light off proceeds by generating (at 414) an ignition heat in at least a portion of the purged oxidizer reactor 224. The manner in which the ignition heat is generated will be implementation specific, e.g., by heating at least a portion of a catalyst bed to at least a light off temperature or actuating a spark source. In the illustrated embodiment, the ignition heat is generated in the catalyst bed 257 (shown in
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The oxidizer light off proceeds by heating (at 418) the oxidizer reactor containing the fuel/air mixture to an operating temperature. An “operating temperature” is a temperature high enough to start and sustain a catalyst reaction of the fuel/air mixture with, e.g., the catalyst bed 257 (shown in
Turning now to
The light off of the ATR 110 continues by (at 424), maintaining the non-pyrophoric shift catalyst (not shown) of the autothermal reformer 110 shift 250 d at a temperature sufficient to prevent condensation of water therein. In the illustrated embodiment, the ATR 110 employs heaters (i.e., the heat exchanger 290, in
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The ATR 110 light off then introducing air 118 (at 428) to the reactor 250 b to produce an air and fuel mixture (not shown) exceeding the upper explosive limit (“UEL”) of the fuel 112. The illustrated embodiment implements the fuel 112 with natural gas, which has a UEL of 17.0% in air, or 1.03 O/C(NG). Thus, the illustrated embodiment introduces air to achieve a concentration of 26% natural gas in air, or an O/C(NG) ratio of 0.6.
The ATR 110 light off concludes by heating (at 430) the reactor 250 b to an operating temperature. In the illustrated embodiment, the operating temperature will be between approximately 600° C. and approximately 900° C., and preferably approximately 700° C. The non-pyrophoric shift catalyst will be maintained at a temperature of approximately 250° C. More detail on the normal operation of the ATR 110 after start-up is provided immediately below.
In normal operation, the processor reactor (not shown) of the ATR 104 reforms the process feed stream 120 into the hydrogen, or hydrogen-enriched, gas stream and effluent byproducts, such as water. The process feed stream 120 in the illustrated embodiment conveys a fuel, air, and water mixture from the oxidizer 114, shown in
The fuel processor 102 process feed stream 120 includes a hydrocarbon fuel, oxygen, and water mixture, as was described above. The oxygen can be in the form of air, enriched air, or substantially pure oxygen. The water can be introduced as a liquid or vapor. The composition percentages of the feed components are determined by the desired operating conditions, as discussed below. The fuel processor effluent stream from of the present invention includes hydrogen and carbon dioxide and can also include some water, unconverted hydrocarbons, carbon monoxide, impurities (e.g., hydrogen sulfide and ammonia) and inert components (e.g., nitrogen and argon, especially if air was a component of the feed stream).
Process step A is an autothermal reforming process in which, in one particular embodiment, two reactions, a partial oxidation (formula I, below) and an optional steam reforming (formula II, below), are performed to convert the feed stream 120 into a synthesis gas containing hydrogen and carbon monoxide. Formulas I and II are exemplary reaction formulas wherein methane is considered as the hydrocarbon:
The operating temperature of the autothermal reforming step A can range from about 550° C. to about 900° C., depending on the feed conditions and the catalyst. The ratios, temperatures, and feed conditions are all examples of parameters controlled by the control system of the present invention. The illustrated embodiment uses a catalyst bed of a partial oxidation catalyst in the reformer with or without a steam reforming catalyst.
Process step B is a cooling step for cooling the synthesis gas stream from process step A to a temperature of from about 200° C. to about 600° C., preferably from about 375° C. to about 425° C., to prepare the temperature of the synthesis gas effluent for the process step C (discussed below). This cooling may be achieved with heat sinks, heat pipes or heat exchangers depending upon the design specifications and the need to recover/recycle the heat content of the gas stream using any suitable type of coolant. For instance, the coolant for process step B may be the coolant 113 of the thermal subsystem 128.
Process step C is a purifying step and employs zinc oxide (ZnO) as a hydrogen sulfide absorbent. One of the main impurities of the hydrocarbon stream is sulfur, which is converted by the autothermal reforming step A to hydrogen sulfide. The processing core used in process step C preferably includes zinc oxide and/or other material capable of absorbing and converting hydrogen sulfide, and may include a support (e.g., monolith, extrudate, pellet, etc.). Desulfurization is accomplished by converting the hydrogen sulfide to water in accordance with the following reaction formula III:
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Process step E is a water gas shift reaction that converts carbon monoxide to carbon dioxide in accordance with formula IV:
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Process step G is an oxidation step wherein almost all of the remaining carbon monoxide in the effluent stream is converted to carbon dioxide. The processing is carried out in the presence of a catalyst for the oxidation of carbon monoxide. Two reactions occur in process step G: the desired oxidation of carbon monoxide (formula V) and the undesired oxidation of hydrogen (formula VI) as follows:
The preferential oxidation of carbon monoxide is favored by low temperatures. Since both reactions produce heat it may be advantageous to optionally include a cooling element such as a cooling coil, disposed within the process. The operating temperature of process is preferably kept in the range of from about 90° C. to about 150° C. Process step G reduces the carbon monoxide level to preferably less than 50 ppm, which is a suitable level for use in fuel cells.
The reformate 105 exiting the fuel processor is a hydrogen rich gas containing carbon dioxide and other constituents which may be present such as water, inert components (e.g., nitrogen, argon), residual hydrocarbon, etc. Product gas may be used as the feed for a fuel cell or for other applications where a hydrogen rich feed stream is desired. Optionally, product gas may be sent on to further processing, for example, to remove the carbon dioxide, water or other components. Table 1 presents additional information on the normal operation of the ATR 110.
Eventually, the operational cycle ends, and the fuel processor 102 is shutdown, as shown in
Turning now to
To shutdown and purge the oxidizer 110, as is shown in
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.